1. Field of the invention
The present invention is generally concerned with clutch release bearings, in particular those for automotive vehicles.
2. Description of the Prior Art
As is known, a clutch release bearing generally comprises an operating member through the intermediary of which it is adapted to be operated on by a control member, in practice a clutch release yoke, and a drive member which is coupled to said operating member by a cover, for example, and through the intermediary of which the clutch release bearing is adapted to operate on the clutch release device of a clutch.
The present invention is more particularly, but not necessarily exclusively, concerned with self-centering clutch release bearings, that is to say clutch release bearings in which the drive member is able to move relative to the operating member perpendicularly to the axis of the assembly wherein self-centering results.
One problem to be overcome in producing clutch release bearings of this type results from the fact that, because their drive member is then in contact with a rotating member, namely the clutch release device of the clutch concerned, they are subjected in service to forces tending to rotate them about their axis.
Any such rotation of the clutch release bearing about its axis in service could not fail to disturb the self-centering action, especially when the self-centering action is "maintained", that is to say when springloaded friction means are provided between the drive member and the operating member.
Thus it is desirable or even essential to prevent the clutch release bearing rotating about its axis in service.
To achieve this it has been proposed to key the clutch release bearing circumferentially to the clutch release yoke which is of course keyed against rotation about the axis of the clutch release bearing by virtue of its being pivotally mounted on the casing of the associated gearbox; when the clutch release bearing comprises a cover with which the clutch release yoke cooperates, it has been proposed to key the operating member circumferentially to the cover.
Concerning the circumferential keying of the clutch release bearing to the clutch release yoke, as the clutch release yoke in practice comprises two fingers through the intermediary of which it is engaged over a clutch release bearing of this kind so as to operate thereon, it has been proposed to employ two axial facets on the clutch release bearing, usually called axial guide facets, extending axially and parallel to each other and therefore adapted to cooperate with respective lateral surfaces of said fingers of the clutch release yoke, these surfaces facing each other.
Axial guide facets like these are not always easy to provide, especially where they must be formed on a cover.
Furthermore, they may themselves give rise to difficulties in certain types of clutch release bearing, more precisely "pull-type" clutch release bearings, that is to say clutch release bearings designed to operate in traction on the clutch release device of the clutch to be controled.
Such traction operation implies, on the one hand, that the drive member of the clutch release bearing is engaged behind the clutch release device of the clutch to be controled, or is engaged with some form of member, a coupling member, for example, itself engaged behind the clutch release device, and, on the other hand, that the clutch release yoke be engaged transversely between the clutch release device and transverse bearing facets provided for this purpose on the clutch release bearing.
In practice the clutch release yoke and the clutch release bearing form parts of two different assemblies, on the one hand that comprising the casing of the gearbox, which carries the clutch release yoke, and on the other hand that comprising the engine block, which usually carries the associated clutch and therefore the clutch release bearing.
At assembly time, that is to say when these two assemblies are brought axially towards each other, it is necessary to engage progressively the fingers of the clutch release yoke behind the transverse bearing facets of the clutch release bearing. However, demounting or disconnection of the two assemblies from each other must be possible for subsequent access to the clutch for changing or overhauling it, for example.
It must then be possible to disengage the clutch release yoke from the clutch release bearing.
The pivoting of the clutch release yoke required to engage it behind the transverse bearing facets of the clutch release bearing at assembly time or to disengage it therefrom at demounting time is not always possible, since it requires a non-negligible dead space which is not always available.
To eliminate such pivoting movements it has been proposed to provide between the clutch release bearing and the clutch release yoke a quarter-turn coupling whereby the clutch release bearing is turned about its axis through an angle sufficient for the transverse bearing facets to escape from the fingers of the clutch release yoke at demounting time, for example, so that they can then be disengaged axially relative thereto.
It is clear that when axial guide facets for the fingers of the clutch release yoke are provided on the clutch release bearing, these axial guide facets oppose rotation of the clutch release bearing about its axis.
Turning now to the circumferential keying of the operating member of the clutch release bearing to the cover, where it comprises a cover, it has been proposed, in particular in U.S. Pat. No. 4 529 075 and in a French patent of addition application filed 15 June 1983 under the number 83 09874 and published under the number 2 533 281 relating to a parent French patent filed 18 June 1981 under the number 81 12001 and published under the number 2 508 125, to exploit elastically deformable lugs (provided for coupling together the cover and the operating member) to procure such circumferential keying.
In practice these elastically deformable lugs form part of the operating member and cooperate with two openings provided for this purpose in the cover, the part cooperating with an opening being complementary thereto in the circumferential direction.
Although giving satisfaction, an arrangement of this kind has the disadvantage of applying non-negligible circumferential loads to the elastically deformable lugs in service.
For them to be able to withstand such loads, they must be made sufficiently thick, which is detrimental to their elasticity.
A general object of the present invention consists in arrangements which, while procuring in a satisfactory way the necessary circumferential retention of the clutch release bearing, make it possible to eliminate the disadvantages outlined hereinabove, conferring also other advantages.